A common method of building construction is to erect a building frame (typically of wood), cover the frame with a layer of building paper on the exterior of the building, and then apply cladding over the building paper. The cladding may be any of a wide variety of materials, e.g. plaster-based preparations, sheets of simulated or synthetic stone, weatherboard, fibre cement or polystyrene.
The frames for windows are set into the framing, and the cladding butts up against the edges of each window frame. The join between the cladding and each vertical side edge of the window frame usually is sealed with a known sealant compound. This technique is capable of providing an efficient seal, but only if the sealant is applied carefully, using the correct technique, and if the underlying materials are clean and dry. Unfortunately, under the sort of conditions which often prevail on building sites, the sealant often is applied incorrectly and/or to poorly prepared underlying materials; this results in an inadequate seal which leaks in use, and this can cause rotting of the building frame.